The present disclosure generally relates to water pumps for vehicles. More specifically, the present disclosure relates to a variable capacity water pump having an electromagnetic control.
Water pumps are typically used on vehicles today to provide heat transfer means for an engine during operation. The engine crank shaft typically drives the water pump at a fixed ratio. Thus, as the engine idle speed is reduced, a trend in vehicles today to reduce emissions, the water pump speed is correspondingly reduced. This reduction in water pump speed results in a reduction of the coolant flow through the cooling system which can result in poor heater output for the interior of the vehicle when needed in cold weather and also can result in poor coolant flow for engine cooling during hot weather.
Increasing the water pump speed by increasing the drive ratio from the crank shaft will increase the coolant flow at engine idle speeds, but it may result in over speeding the water pump at higher engine speeds which may produce pump cavitations and reduced water pump bearing life. Pump cavitations can result in pump damage and a reduction in cooling system performance.
It is known to add an auxiliary water pump, typically electrically driven, to provide additional coolant at low engine idle speeds. Another approach is to use movable vanes in the inlet of the water pump to throttle the coolant flow at higher engine speeds. However, the prior art systems have numerous disadvantages. For example, the auxiliary water pump and electrically driven water pump can add weight and cost because extra components are required, and because the capacity of the battery and generator needs to be increased, to supply the extra power needed by the water pump motor.
The present disclosure provides a variable capacity water pump having good coolant flow at low engine idle speeds while avoiding pump cavitation at higher engine speeds and without the need for an auxiliary water pump.